Avian pet species survives controlled WNV infection

While the American Crow is a known West Nile Virus (WNV) carrier, researchers are focused on whether rarely observed species, such as the psittacine, are also at risk, and whether a vaccine for horses has application in psittacines.

Two independent bird studies are under way - the first not-yet-publishedreport is being finalized at the Centers for Disease Control and Preventionin Fort Collins, Colo., the second is a private practitioner's undertakingin Florida.

The CDC study takes an exhaustive look at WNV's effect on 23 bird species,and for the first time, devotes attention to the psittacine family, whichincludes cockatoos, parrots and parakeets.

West Nile virus, a risk to public, equine and animal health, can be manifestedin fatal encephalitis in humans and horses, as well as mortality in certaindomestic and wild birds.

"We don't really fully understand the effects of WNV on the healthof these psittacine birds," says Nicholas Komar, Sc.D., lead researcherfor the CDC study.

The experimental infection of psittacines involves three birds each oftwo species: the South American native monk parakeet, (the Quaker parrot),a popular pet in the United States, and another common pet, the Australia-nativebudgerigar or parakeet, according to Komar. Both species have colonizedmajor cities in states including Florida, Illinois and Texas.

"We were hoping that these two species would represent the psittacinesin general," says Komar. "But that may not be the case."

The six birds were infected by mosquito bite, a Culex variety, but notthe species that is considered a vector in the United States.

"We found that the viremia in the blood that develops is very low,"says Komar. "It does not develop infectious titers, which means thatthe amount of virus particles in the blood is insufficient to then infecta mosquito.

"So that's good news," he says.

Additional good news: researchers detected no trace of illness, and allbirds survived the infection. "In this small number of birds that weexperimentally infected, they seem to be pretty hardy," Komar says.

Prior to the study, there were some reports of dead pet psittacines withWest Nile virus detected in them in New York State for example, accordingto Komar. Some species included cockatiels, cockatoos, parakeets and macaws.

Whether WNV was the sole or contributory cause is not yet known, he says.

"To what extent those birds are really at risk is really hard tosay," Komar says. "It could be that WNV infection on top of otherconditions could be fatal, for example malnutrition or other infectionsundetected or old age."

Part of larger study

As for the other 22 species under observation, Komar says, the work isbeing conducted "to better understand which bird species may be involvedin the transmission cycle. In particular passerine birds (i.e., house sparrow)seem to be the most important."

All birds were easily infected, but only certain birds developed enoughvirus in the blood to be able to infect mosquitoes. A high rate of mortalitywas observed especially in the corvids, he says.

Komar confirmed some surprise finding in the study, but declined to elaborateat this time.

The goal of the research is simple, says Komar. "If you can identifythe important reservoir hosts in a particular region, then you can designyour surveillance strategies around that information."

The study is expected to be published within six months.

Psittacines, part II

Along with other avian private practitioners, Dr. Susan Clubb, dipl.American Board of Veterinary Practitioners, in Loxahatchee, Fla., is conductingan avian vaccination study, using the Fort Dodge Animal Health USDA-approvedequine WNV vaccine. The study, launched in December 2001, is testing 59psittacines (plus two turacos and one toucanette).

Birds were housed outdoors in Palm Beach and Miami-Dade counties. Speciesincluded macaws, cockatoos, Amazons, conures, cockatiels, African greysand Quaker parakeets.

All birds were bled at the time of the initial vaccination to establisha baseline of exposure, according to Clubb.

After three weeks, they were bled again for the second vaccination. Athird blood sample was collected three weeks after the second dose of vaccine.Dosage and route of administration varied.

"Vaccinated psittacines developed WNV-neutralizing antibodies, asmeasured by the standard plaque reduction neutralization test," saysClubb. "Induction of significant neutralizing antibody levels givesa reasonable expectation of efficacy however challenge studies were notpreformed."

The results are still being analyzed, according to Clubb who adds, "initialimpressions are good." The best results were noted with a low dose(.25 ml) administered subcutaneously.

The birds presented no adverse reactions.

Conclusions

Preliminary observations suggest that West Nile virus is a health riskfor psittacines but morbidity and mortality rates appear to be very low,Clubb says.

Older birds appear to be more severely affected, according to her research.

"Establishing a definitive diagnosis for West Nile disease has beenchallenging," Clubb says. "Virus isolation has been unrewardingwhich might indicate transient infections occur in psittacines. Severalcases exhibiting acute onset of clinical signs were seropositive indicationpossibly of rapid seroconversion."

First impressions of vaccine efficacy are "promising," saysClubb, adding that birds exhibited no adverse reactions upon vaccination.

In cases where indicated, Clubb says, "vaccination is a viable option."